Significance Much work remains to be accomplished to determine the organization of brain regions that subserve learning and memory. Once the circuitry of learning and memory is established, other techniques may probe these brain regions to determine ways to facilitate learning and memory and perhaps to restore function in degenerative disorders such as Alzheimer[unreadable]s disease. Objectives This program is designed to provide a comprehensive understanding of the inputs, outputs and intrinsic circuitry of memory-related structures such as the hippocampus. Many of the brain regions that are connected with the hippocampus and subserve normal memory function in the human and nonhuman primate, are not found in the rodent brain. Results This is a multifaceted program of studies. We have used intracellular techniques to study the three dimensional organization of neurons in the hippocampal formation. We have used tracing techniques to map the connections of the hippocampus and related structures. During the current year we have focused our efforts on the retrosplenial region of the cingulate gyrus. We have also used immunohistochemical and in situ hybridization techniques to determine the chemical identity of various pathways in the hippocampal formation. Future Directions We will begin detailed, and where possible, quantitative comparisons of the hippocampal formation in the human and nonhuman primate. These studies will employ molecular neuroanatomical techniques to mark similar categories of neurons and neural connections in the brains of both species. KEYWORDS memory, neuroanatomy